In optical communications, optical signals carry information. For example, a transmitter (e.g., a laser or laser diode) in an optical or optoelectronic transceiver converts one or more electrical signals into optical signals, and a receiver (e.g., a photodiode) in an optical or optoelectronic transceiver converts one or more optical signals into electrical signals. One objective of optical communication research and development is to increase and/or maximize bandwidth (e.g., the amount of information transmitted) to the greatest extent possible. Another objective is to communicate the information with as few errors or losses as possible.
In a number of conventional designs, the optics in an optical or optoelectronic transceiver includes a filter at a 45° angle relative to the incoming optical signal and a photodetector at a 90° angle relative to the incoming optical signal. The filter reflects the incoming optical signal towards the photodetector. FIG. 1 shows such a conventional optical receiver 100, including a lens 110, a mirror 120, a filter 130, and a receiver 140. As shown, lens 110 receives an optical signal IN (e.g., from an optical fiber) and provides a focused optical signal 150 to the mirror 120. The mirror 120 then reflects the optical signal 150 to the receiver 140 in the form of a reflected optical signal 155 for further processing. The reflected optical signal 155 may pass through the filter 130 before being received in the receiver 140. The reflected optical signal 155 may be partially or fully polarized (e.g., having electric field vectors in planes at certain angles with reduced amplitudes).
In a bidirectional optical transceiver, the mirror 120 is replaced with a filter (e.g., a wavelength selective filter). In such a case, the filter in the path of the optical signal may cause a significant loss in received signal power (e.g., filter insertion loss). Increasing the power of the received optical signal 150 at the source can exceed the specifications of other components in an optical system (such as an optical network) including the bidirectional optical transceiver.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.